Characteristics required for a magnetic disk mounted in an HDD of a magnetic recording system or the like include, for example, a good SNR of a recorded signal, good thermal stability, and easiness to record. Among others, in order to improve a SNR, it is necessary to reduce the particle diameter of magnetic particles constituting a magnetic recording layer. However, if the particle diameter of magnetic particles is reduced, a signal becomes thermally unstable. In order to thermally stabilize a signal, it is necessary to increase perpendicular magnetic anisotropy energy (Ku), however, if perpendicular magnetic anisotropy energy is increased too much, it becomes impossible to record information on a magnetic head.
In order to solve such a problem, for example, a CGC (Continuous Granular Coupled) medium has been developed, which comprises a granular magnetic recording layer composed of granular columnar particles and non-magnetic regions between the granular columnar particles; and an auxiliary recording layer formed on the granular magnetic recording layer and causing exchange coupling among the granular columnar particles. In the CGC medium, static magnetic characteristics (SNR), recording characteristics, and thermal stability can be controlled by adjusting the exchange interaction between the auxiliary recording layer and the granular magnetic recording layer, and the exchange interaction among the granular columnar particles via the auxiliary recording layer.